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Wed, 22 Feb 2006 17:03:54 +0100Wed, 22 Feb 2006 17:03:54 +0100"Antiflow" of antiprotons in heavy ion collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2962
In the framework of the relativistic quantum dynamics approach we investigate antiproton observables in Au-Au collisions at 10.7A GeV. The rapidity dependence of the in-plane directed transverse momentum p(y) of p's shows the opposite sigh of the nucleon flow, which has indeed recently been discovered at 10.7A GeV by the E877 group. The "antiflow" of p's is also predicted at 2A GeV and at 160 A GeV and appears at all energies also for pi's and K's. These predicted p anticorrelations are a direct proof of strong p annihilation in massive heavy ion reactions.André Jahns; Christian Spieles; Heinz Sorge; Horst Stöcker; Walter Greinerarticlehttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2962Wed, 22 Feb 2006 17:03:54 +0100High pT pions as probes of the dense phase of relativistic heavy ion collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2959
The properties of pions from the hot and dense reaction stage of relativistic heavy ion collisions are investigated with the quantum molecular dynamics model. Pions originating from this reaction stage stem from resonance decay with enhanced mass. They carry high transverse momenta. The calculation shows a direct correlation between high pt pions, early freeze-out times and high freeze-out densities.S. A. Bass; C. Hartnack; Horst Stöcker; Walter Greinerarticlehttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2959Wed, 22 Feb 2006 16:56:11 +0100Pion and thermal photon spectra as a possible signal for a phase transitionhttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2957
We calculate thermal photon and neutral pion spectra in ultrarelativistic heavy-ion collisions in the framework of three-fluid hydrodynamics. Both spectra are quite sensitive to the equation of state used. In particular, within our model, recent data for S + Au at 200 AGeV can only be understood if a scenario with a phase transition (possibly to a quark-gluon plasma) is assumed. Results for Au+Au at 11 AGeV and Pb + Pb at 160 AGeV are also presented.Adrian Dumitru; Ulrich Katscher; Joachim A. Maruhn; Horst Stöcker; Walter Greiner; Dirk-Hermann Rischkepreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2957Wed, 22 Feb 2006 16:50:36 +0100A Stopped delta-matter source in heavy ion collisions at 10-GeV/N?http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2956
We predict the formation of highly dense baryon-rich resonance matter in Au+Au collisions at AGS energies. The final pion yields show observable signs for resonance matter. The Delta1232 resonance is predicted to be the dominant source for pions of small transverse momenta. Rescattering e ects consecutive excitation and deexcitation of Delta's lead to a long apparent life- time (> 10 fm/c) and rather large volumina (several 100 fm3) of the Delta-matter state. Heavier baryon resonances prove to be crucial for reaction dynamics and particle production at AGS.Markus Hofmann; Raffaele Mattiello; Heinz Sorge; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2956Wed, 22 Feb 2006 16:47:51 +0100Baryon-antibaryon pair production in time-dependent meson fieldshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2955
Strong mean meson fields, which are known to exist in normal nuclei, experience a violent deformation in the course of a heavy-ion collision at relativistic energies. This may give rise to a new collective mechanism of the particle production, not reducible to the superposition of elementary nucleon-nucleon collisions.Igor N. Mishustin; Leonid M. Satarov; Horst Stöcker; Walter Greinerarticlehttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2955Wed, 22 Feb 2006 16:43:11 +0100pi-N correlations probe the nuclear equation of state in relativistic heavy ion-collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2953
We investigate the sensivity of pionic bounce-off and squeeze-out on the density and momentum dependence of the real part of the nucleon optical potential. For the in-plane pion bounce-off we find a strong sensivity on both the density and momentum dependence whereas the out-of-plane pion squeeze-out shows a strong sensivity only towards the momentum dependence but little sensivity towards the density dependence.S. A. Bass; C. Hartnack; Horst Stöcker; Walter Greinerarticlehttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2953Wed, 15 Feb 2006 16:32:49 +0100Bose stimulated pion production in relativistic nuclear collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2952
We demonstrate the importance of the Bose-statistical effects for pion production in relativistic heavy-ion collisions. The evolution of the pion phase-space density in central collisions of ultrarelativistic nuclei is studied in a simple kinetic model taking into account the effect of Bose-simulated pion production by the NN collisions in a dense cloud of mesons.Igor N. Mishustin; Leonid M. Satarov; Joachim A. Maruhn; Horst Stöcker; Walter Greinerarticlehttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2952Wed, 15 Feb 2006 16:26:33 +0100Azimuthal correlations of pions in relativistic heavy ion collisions at 1 GeV/nucl.http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2945
Triple differential cross sections of pions in heavy ion collisions at 1 GeV/nucl. are studied with the IQMD model. After discussing general properties of resonance and pion production we focus on azimuthal correlations: At projectile- and target-rapidities we observe an anticorrelation in the in-plane transverse momentum between pions and protons. At c.m.-rapidity, however, we find that high pt pions are being preferentially emitted perpendicular to the event-plane. We investigate the causes of those correlations and their sensitivity on the density and momentum dependence of the real and imaginary part of the nucleon and pion optical potential.Steffen A. Bass; Christoph Hartnack; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2945Fri, 10 Feb 2006 16:39:55 +0100On the impossibility of temperature extraction from heavy ion induced particle spectrahttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2967
Spectra of various particle species have been calculated with the Quantum Molecular Dynamics (QMD) model for very central collisions of Au+Au. They are compatible with the idea of a fully stopped thermal source which exhibits a transversal expansion besides the thermal distribution of an ideal gas. How- ever, the microscopic analyses of the local flow velocities and temperatures indicate much lower temperatures at densities associated with the freeze-out. The results express the overall impossibility of a model-independent determi- nation of nuclear temperatures from heavy ion spectral data, also at other energies (e.g. CERN) or for other species (i.e. pions, kaons, hyperons)Jens Konopka; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2967Wed, 08 Feb 2006 11:31:34 +0100Neural networks for impact parameter determinationhttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2992
Abstract: An accurate impact parameter determination in a heavy ion collision is crucial for almost all further analysis. The capabilities of an artificial neural network are investigated to that respect. A novel input generation for the network is proposed, namely the transverse and longitudinal momentum distribution of all outgoing (or actually detectable) particles. The neural network approach yields an improvement in performance of a factor of two as compared to classical techniques. To achieve this improvement simple network architectures and a 5 × 5 input grid in (pt, pz) space are suffcient.Steffen A. Bass; A. Bischoff; Joachim A. Maruhn; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2992Mon, 23 Jan 2006 10:34:14 +0100Nucleus-nucleus collisions at highest energieshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2991
The microscopic phasespace approach URQMD is used to investigate the stopping power and particle production in heavy systems at SPS and RHIC energies. We find no gap in the baryon rapidity distribution even at RHIC. For CERN energies URQMD shows a pile up of baryons and a supression of multi-nucleon clusters at midrapidity.Marcus Bleicher; N. Amelin; Steffen A. Bass; Mathias Brandstetter; Adrian Dumitru; Christoph Ernst; Lars Gerland; Jens Konopka; Christian Spieles; Henning Weber; L. A. Winckelmann; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2991Mon, 23 Jan 2006 10:08:06 +0100Particle production by time-dependent meson fields in relativistic heavy ion-collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3006
According to the Walecka mean field theory of nuclear interaction the collective mutual deceleration of the colliding nuclei gives rise to the bremsstrahlung of real and virtual ! mesons. It is shown that decays of these mesons may give a noticeable contribution to the observed yields of the baryon antibaryon pairs, dileptons and pions. Excitation functions and rapidity distributions of particles produced by this mechanism are calculated under some simplifying assumptions about the space time variation of meson fields in nuclear collisions. The calculated multiplicities of coherently produced particles grow fast with the bombarding energy, reaching a saturation above the RHIC bombarding energy. In the case of central Au+Au collisions the bremsstrahlung mechanism becomes comparable with particle production in incoherent hadron hadron collisions above the AGS energies. The rapidity spectra of antibaryons and pions exhibit a characteristic two hump structure which is a consequence of incomplete projectile target stopping at the initial stage of the reaction. The predicted distribution of e+e pairs has a strong peak at invariant masses Me+e < 0.5 GeV.Igor N. Mishustin; Leonid M. Satarov; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3006Thu, 19 Jan 2006 14:02:04 +0100"Pressure equilibration" in ultrarelativistic heavy ion collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/4576
We study the time scale for pressure equilibration in heavy ion collisions at AGS energies within the three-fluid hydrodynamical model and a microscopic cascade model (UrQMD). We find that kinetic equilibrium is reached in both models after a time of 5 fm/c (center-of-mass time). Thus, observables which are sensitive to the early stage of the reaction differ considerably from the expectations within the instant thermalization scenario (one-fluid hydrodynamical model).Jörg Brachmann; Adrian Dumitru; Christian Spieles; Joachim A. Maruhn; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/4576Thu, 19 Jan 2006 13:53:26 +0100Modelling the many-body dynamics of heavy ion collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3010
Basic problems of the semiclassical microscopic modelling of strongly interacting systems are discussed within the framework of Quantum Molecular Dynamics (QMD). This model allows to study the influence of several types of nucleonic interactions on a large variety of observables and phenomena occur- ring in heavy ion collisions at relativistic energies. It is shown that the same predictions can be obtained with several numerically completely di erent and independently written programs as far as the same model parameters are employed and the same basic approximations are made. Many observ- ables are robust against variations of the details of the model assumptions used. Some of the physical results, however, depend also on rather technical parameters like the preparation of the initial configuration in phase space. This crucial problem is connected with the description of the ground state of single nuclei, which di ers among the various approaches. An outlook to an improved molecular dynamics scheme for heavy ion collisions is given.Christoph Hartnack; Rajeev Kumar Puri; Jörg Aichelin; Jens Konopka; Steffen A. Bass; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3010Tue, 17 Jan 2006 10:10:35 +0100"Soft'' transverse expansion and flow in a multi-fluid model without phase transitionhttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3009
Abstract: We study transverse expansion and directed flow in Au(11AGeV)Au reactions within a multi-fluid dynamical model. Although we do not employ an equation of state (EoS) with a first order phase transition, we find a slow increase of the transverse velocities of the nucleons with time. A similar behaviour can be observed for the directed nucleon flow. This is due to non-equilibrium e ects which also lead to less and slower conversion of longitudinal into transverse momentum. We also show that the proton rapidity distribution at CERN energies, as calculated within this model, agrees well with the preliminary NA44-data.Jörg Brachmann; Adrian Dumitru; Marcus Bleicher; Joachim A. Maruhn; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3009Tue, 17 Jan 2006 10:01:46 +0100Nonequilibrium fluid-dynamics in the early stage of ultrarelativistic heavy-ion collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3008
To describe ultrarelativistic heavy-ion collisions we construct a three-fluid hydrodynamical model. In contrast to one-fluid hydrodynamics, it accounts for the finite stopping power of nuclear matter, i.e. for nonequilibrium e ects in the early stage of the reaction. Within this model, we study baryon dynamics in the BNL-AGS energy range. For the system Au+Au we find that kinetic equilibrium between projectile and target nucleons is established only after a time teq CM H 5 fm/c C 2RAu/³CM. Observables which are sensitive to the early stage of the collision (like e.g. nucleon flow) therefore di er considerably from those calculated in the one-fluid model.Jörg Brachmann; Adrian Dumitru; Joachim A. Maruhn; Horst Stöcker; Walter Greiner; Dirk-Hermann Rischkepreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3008Tue, 17 Jan 2006 09:57:57 +0100Probes for the early reaction dynamics of heavy ion collisions at AGS and SPShttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3022
We discuss the early evolution of ultrarelativistic heavy-ion collisions within a multi- fluid dynamical model. In particular, we show that due to the finite mean-free path of the particles compression shock waves are smeared out considerably as compared to the one-fluid limit. Also, the maximal energy density of the baryons is much lower. We discuss the time scale of kinetic equilibration of the baryons in the central region and its relevance for directed flow. Finally, thermal emission of direct photons from the fluid of produced particles is calculated within the three-fluid model and two other simple expansion models. It is shown that the transverse momentum and rapidity spectra of photons give clue to the cooling law and the early rapidity distribution of the photon source.Adrian Dumitru; Jörg Brachmann; Marcus Bleicher; Joachim A. Maruhn; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3022Mon, 16 Jan 2006 10:45:00 +0100A Microscopic calculation of secondary Drell-Yan production in heavy ion collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3040
A study of secondary Drell-Yan production in nuclear collisions is presented for SPS energies. In addition to the lepton pairs produced in the initial collisions of the projectile and target nucleons, we consider the potentially high dilepton yield from hard valence antiquarks in produced mesons and antibaryons. We calculate the secondary Drell-Yan contributions taking the collision spectrum of hadrons from the microscopic model URQMD. The con- tributions from meson-baryon interactions, small in hadron-nucleus interac- tions, are found to be substantial in nucleus-nucleus collisions at low dilepton masses. Preresonance collisions of partons may further increase the yields.Christian Spieles; Lars Gerland; Nils Hammon; Marcus Bleicher; Steffen A. Bass; Horst Stöcker; Walter Greiner; Carlos Lourenco; Ramona Vogtpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3040Thu, 05 Jan 2006 09:42:26 +0100Relativistic transport theory of N, Delta and N* (1440) interacting through sigma, omega and pi mesons.http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3048
A self-consistent relativistic integral-di erential equation of the Boltzmann- Uehling-Uhlenbeck-type for the N*(1440) resonance is developed based on an effective Lagrangian of baryons interacting through mesons. The closed time-path Green s function technique and semi-classical, quasi-particle and Born approxima- tions are employed in the derivation. The non-equilibrium RBUU-type equation for the N*(1440) is consistent with that of nucleon s and delta s which we derived before. Thus, we obtain a set of coupled equations for the N,Delta and N*(1440) distribution functions. All the N (1440)-relevant in-medium two-body scattering cross sections within the N,Delta and N*(1440) system are derived from the same effective Lagrangian in addition to the mean field and presented analytically, which can be directly used in the study of relativistic heavy-ion collisions. The theoreticalprediction of the free pp - pp* (1440) cross section is in good agreement with the experimental data. We calculate the in-medium N+N - N+N* , N* +N - N+N and N*+N - N* +N cross sections in cold nuclear matter up to twice the nuclear matter density. The influence of different choices of the N* N* coupling strengths, which can not be obtained through fitting certain experimental data, are discussed. The results show that the density dependence of predicted in-medium cross sections are sensitive to the N* N* coupling strengths used. An evident density dependence will appear when a large scalar coupling strength of g^(sigma) N*N* is assumed. PACS number(s): 24.10.Cn; 25.70.-z; 21.65.+fGuangjun Mao; Ludwig Neise; Horst Stöcker; Walter Greiner; Zhuxia Lipreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3048Wed, 21 Dec 2005 11:00:59 +0100Dilepton production by bremsstrahlung of meson fields in nuclear collisionshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3065
We study the bremsstrahlung of virtual omega mesons due to the collective deceleration of nuclei at the initial stage of an ultrarelativistic heavy ion collision. It is shown that electromagnetic decays of these mesons may give an important contribution to the observed yields of dileptons. Mass spectra of e+e and µ+µ pairs produced in central Au+Au collisions are calculated under some simplifying assumptions on the space time variation of the baryonic current in a nuclear collision process. Comparison with the CERES data for 160 AGev Pb+Au collisions shows that the proposed mechanism gives a noticeable fraction of the observed e+e pairs in the intermediate region of invariant masses. Sensi tivity of the dilepton yield to the in medium modification of masses and widths of vector mesons is demonstrated.Igor N. Mishustin; Leonid M. Satarov; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3065Mon, 19 Dec 2005 13:10:58 +0100Nuclear shadowing effects on prompt photons at RHIC and LHChttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3068
The transverse momentum distribution of prompt photons coming from the very early phase of ultrarelativistic heavy ion collisions for the RHIC and LHC energies is calculated by means of perturbative QCD. We calculate the single photon cross section (A + B -> gamma + X) by taking into account the partonic sub processes q + q -> gamma + g and q + g -> gamma + q as well as the Bremsstrahlung corrections to those processes. We choose a lower momentum cut-off k0 = 2 GeV separating the soft physics from perturbative QCD. We compare the results for those primary collisions with the photons produced in reactions of the thermalized secondary particles, which are calculated within scaling hydrodynamics. The QCD processes are taken in leading order. Nuclear shadowing corrections, which alter the involved nuclear structure functions are explicitly taken into account and compared to unshadowed results. Employing the GRV parton distribution parametrizations we find that at RHIC prompt QCD-photons dominate over the thermal radiation down to transverse momenta kT &#8776; 2 GeV. At LHC, however, thermal radiation from the QGP dominates for photon transverse momenta kT &#8804; 5 GeV, if nuclear shadowing effects on prompt photon production are taken into account.Nils Hammon; Adrian Dumitru; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3068Thu, 15 Dec 2005 11:57:16 +0100Direct photons in Pb+Pb at CERN-SPS from microscopic transport theoryhttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3075
Direct photon production in central Pb+Pb collisions at CERN-SPS energy is calculated within the relativistic microscopic transport model UrQMD, and within distinctly di erent versions of relativistic hydrodynamics. We find that in UrQMD the local momentum distributions of the secondaries are strongly elongated along the beam axis initially. Therefore, the preequilibrium contribution dominates the photon spectrum at transverse momenta above H 1.5 GeV. The hydrodynamics prediction of a strong correlation between the temperature and radial expansion velocities on the one hand and the slope of the transverse momentum distribution of direct photons on the other hand thus is not recovered in UrQMD. The rapidity distribution of direct photons in UrQMD reveals that the initial conditions for the longitudinal expansion of the photon source (the meson fluid ) resemble rather boostinvariance than Landau-like flow.Adrian Dumitru; Marcus Bleicher; Steffen A. Bass; Christian Spieles; Ludwig Neise; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3075Thu, 15 Dec 2005 11:52:03 +0100Relativistic quantum transport theory of hadronic matter: the coupled nucleon, delta and pion systemhttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3079
We derive the relativistic quantum transport equation for the pion distribution function based on an effective Lagrangian of the QHD-II model. The closed time-path Green s function technique, the semi-classical, quasiparticle and Born approximation are employed in the derivation. Both the mean field and collision term are derived from the same Lagrangian and presented analytically. The dynamical equation for the pions is consistent with that for the nucleons and deltas which we developed before. Thus, we obtain a relativistic transport model which describes the hadronic matter with N,Delta and pi degrees of freedom simultaneously. Within this approach, we investigate the medium e ects on the pion dispersion relation as well as the pion absorption and pion production channels in cold nuclear matter. In contrast to the results of the non-relativistic model, the pion dispersion relation becomes harder at low momenta and softer at high momenta as compared to the free one, which is mainly caused by the relativistic kinetics. The theoretically predicted free pi*N -> Delta cross section is in agreement with the experimental data. Medium e ects on the pi*N -> Delta cross section and momentum-dependent Delta-decay width are shown to be substantial. PACS number(s): 24.10.Cn; 13.75.Cs; 21.65.+f; 25.70.-zGuangjun Mao; Ludwig Neise; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3079Wed, 14 Dec 2005 13:38:24 +0100Can momentum correlations proof kinetic equilibration in heavy ion collisions at 160/A-GeV?http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3080
We perform an event-by-event analysis of the transverse momentum distribution of final state particles in central Pb(160AGeV)+Pb collisions within a microscopic non-equilibrium transport model (UrQMD). Strong influence of rescattering is found. The extracted momentum distributions show less fluctuations in A+A collisions than in p+p reactions. This is in contrast to simplified p+p extrapolations and random walk models.Marcus Bleicher; Mohamed Belkacem; Christoph Ernst; Henning Weber; Lars Gerland; Christian Spieles; Steffen A. Bass; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3080Wed, 14 Dec 2005 13:32:36 +0100Charmonium suppression from purely geometrical effectshttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3096
The extend to which geometrical effects contribute to the production and suppression of the J/psi and qq minijet pairs in general is investigated for high energy heavy ion collisions at SPS, RHIC and LHC energies. For the energy range under investigation, the geometrical e ects referred to are shadowing and anti-shadowing, respectively. Due to those effects, the parton distributions in nuclei deviate from the naive extrapolation from the free nucleon result; fA 6= AfN. The strength of the shadowing/anti-shadowing e ect increases with the mass number. Therefore it is interesting to see the di erence between cross sections for e.g. S+U vs. Pb+Pb at SPS. The recent NA50 results for the survival probability of produced J/psi s has attracted great attention and are often interpreted as a signature of a quark gluon plasma. This publication will present a fresh look on hard QCD e ects for the charmonium production level. It is shown that the apparent suppression of J/psi s must also be linked to the production process. Due to the uncertainty in the shadowing of gluons the suppression of charmonium states might not give reli- able information on a created plasma phase at the collider energies soon available. The consequences of shadowing e ects for the xF distribution of J/psi s at s = 20 GeV, s = 200 GeV and s = 6 TeV are calculated for some relevant combinations of nuclei, as well as the pT distribution of minijets at midrapidity for Nf = 4 in the final state.Nils Hammon; Lars Gerland; Horst Stöcker; Walter Greinerpreprinthttp://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3096Mon, 12 Dec 2005 09:55:25 +0100